bluuebunny/crossref_metadata_2025 huggingface dataset:
Noninterest Income and Financial Performance at U.S. Commercial Banks
Authors: DeYoung Robert , Rice Tara
Published: December 2004

Noninterest income now accounts for over 40% of operating income in the U.S. commercial banking industry. This paper demonstrates a number of empirical links between bank noninterest income, business strategies, market conditions, technological change, and financial performance between 1989 and 2001. The results indicate that well‐managed banks expand more slowly into noninterest activities, and that marginal increases in noninterest income are associated with poorer risk‐return tradeoffs on average. These findings suggest that noninterest income is coexisting with, rather than replacing, interest income from the intermediation activities that remain banks' core financial services function.
Adenovirus as an emerging pathogen in immunocompromised patients
Authors: Leen Ann M. , Rooney Cliona M.
Published: December 2004

Adenoviruses are non‐enveloped, lytic, DNA viruses capable of infecting most animal species. There are 51 different human adenovirus serotypes, which are grouped from A to F on the basis of genome size, composition, homology and organization. Pathogenicity varies according to group and type, but infections are generally well controlled by the host immune system in immunocompetent individuals. However, in the immunosuppressed, adenoviral infections are a frequent cause of morbidity and mortality. To date there is no effective therapy. Adoptive transfer of immune T cells offers a therapeutic option, but this strategy has been hindered by the lack of information on targets of protective cellular immunity, and by the immunological heterogeneity of the 51 human adenoviruses. Nevertheless, until such an approach is implemented, or an effective antiviral agent becomes commercially available, it is likely that adenovirus infections will continue to be responsible for a significant number of virus‐associated deaths each year.
The role of allogeneic transplantation in non‐Hodgkin's lymphoma
Authors: Peggs Karl S. , Mackinnon Stephen , Linch David C.
Published: December 2004

The evolution of combination chemotherapy regimens, combined with improvements in supportive care, has incrementally improved survival outcomes for patients with non‐Hodgkin's lymphomas (NHL). Although 40–60% of younger patients with diffuse large cell lymphoma can now expect to be cured, significant numbers will either fail to achieve a remission or relapse after attaining a remission. In addition, certain histological subtypes are associated with particularly poor prognoses with combination chemotherapy alone (e.g. mantle cell lymphoma, B‐cell prolymphocytic leukaemia). Relatively few of these patients can achieve long‐term responses. Other NHL subtypes, whilst associated with more favourable prognoses in terms of overall survival, are rarely, if ever, cured (e.g. most low grade NHL including follicular lymphoma, chronic lymphocytic leukaemia and small lymphocytic lymphoma). For these reasons dose escalation and allogeneic transplantation have been investigated as potential ways of improving outcome, although this has mainly been in the setting of advanced disease. Any possible benefits have frequently been out‐weighed by procedural morbidity and mortality. The parallel development of transplantation approaches that limit procedural toxicity along with advances in supportive care require that the role of allogeneic haematopoietic stem cell transplantation in the management of lymphoma be re‐evaluated.
Expression of functional interleukin‐21 receptor on adult T‐cell leukaemia cells
Authors: Ueda Maki , Imada Kazunori , Imura Akihiro , Koga Hikari , Hishizawa Masakatsu , Uchiyama Takashi
Published: December 2004

Adult T‐cell leukaemia (ATL) is caused by human T‐cell leukaemia virus type I (HTLV‐I). It has been suggested that cytokines play a role in the development and in the neoplastic cell growth of ATL. However, the precise mechanism involved in this process still remains unclear. Interleukin‐21 (IL‐21) and its receptor (IL‐21R) have been recently described. In this study, we examined the expression of IL‐21R and the effect of IL‐21 on ATL cells. Real‐time reverse transcription polymerase chain reaction showed that HTLV‐I‐infected cell lines and primary ATL cells expressed IL‐21R mRNA. Cell surface expression of IL‐21R on these cells was confirmed by flow cytometric analysis using a newly developed monoclonal antibody against human IL‐21R. In contrast to the expression of IL‐21R, IL‐21 mRNA was scarcely detectable in these cells. Notably, IL‐21 induced the proliferation of ATL‐43T and ED‐40515(+) cells, both of which were derived from leukaemic cell clones of ATL. Concerning the intracellular signalling pathways, IL‐21 activated the phosphorylation of the signal transducers and activators of transcription (STAT)3 and STAT5. Taken together, these findings provide the first evidence that ATL cells express functional IL‐21R, suggesting that it may contribute to the pathophysiology of ATL. In addition, the IL‐21/IL‐21R system may represent a new target for the treatment of ATL.
Response to chemotherapy and treating institution predict survival in primary central nervous system lymphoma
Authors: Korfel Agnieszka , Martus Peter , Nowrousian Mohammad R. , Hossfeld Dieter K. , Kirchen Heinz , Brücher Joachim , Stelljes Matthias , Birkmann Josef , Peschel Christian , Pasold Rita , Fischer Lars , Jahnke Kristoph , Thiel Eckhard ,   the German primary central nervous system lymphoma Study Group (G‐PCNSL‐SG)
Published: December 2004

The majority of the available data on primary central nervous system lymphoma (PCNSL) derive from small unicentric or oligocentric studies. In this multicentre study, we evaluated the response, survival and toxicity in PCNSL patients after carmustine, methotrexate 1·5 g/m2, procarbazine and dexamethasone (BMPD) chemotherapy and searched for prognostic factors. Fifty‐six patients received the BMPD protocol (dexamethasone was given only in course 1). The overall complete response rate to chemotherapy was 61% (34/56). Ten complete responders received whole‐brain irradiation and 24 were not irradiated. Responders to chemotherapy had significantly longer median overall survival than non‐responders (18·2 vs. 9·9 months, P = 0·02). Median survival was significantly longer at institutions accruing at least four patients than at those with fewer patients (31·5 vs. 9·5 months, P = 0·03).
Molecular mechanisms whereby immunomodulatory drugs activate natural killer cells: clinical application
Authors: Hayashi Toshiaki , Hideshima Teru , Akiyama Masaharu , Podar Klaus , Yasui Hiroshi , Raje Noopur , Kumar Shaji , Chauhan Dharminder , Treon Steven P. , Richardson Paul , Anderson Kenneth C.
Published: December 2004

Thalidomide and immunomodulatory drugs (IMiDs), which target multiple myeloma (MM) cells and the bone marrow microenvironment, can overcome drug resistance. These agents also have immunomodulatory effects. Specifically, we have reported that thalidomide increased serum interleukin‐2 (IL‐2) levels and natural killer (NK) cell numbers in the peripheral blood of responding MM patients. In this study, we investigated the mechanisms whereby IMiDs augment NK cell cytotoxicity. NK cytotoxicity and antibody‐dependent cell‐mediated cytotoxicity (ADCC) of peripheral blood mononuclear cells cultured with IMiDs were examined in the presence or absence of anti‐IL‐2 antibody, ciclosporin A or depletion of CD56‐positive cells. IMiDs‐induced signalling pathways, triggering IL‐2 transcription in T cells, were also delineated. IMiDs facilitated the nuclear translocation of nuclear factor of activated T cells‐2 and activator protein‐1 via activation of phosphoinositide‐3 kinase signalling, with resultant IL‐2 secretion. IMiDs enhanced both NK cell cytotoxicity and ADCC induced by triggering IL‐2 production from T cells. These studies defined the mechanisms whereby IMiDs trigger NK cell‐mediated tumour‐cell lysis, further supporting their therapeutic use in MM.
Patient self‐testing is a reliable and acceptable alternative to laboratory INR monitoring
Authors: Gardiner Chris , Williams Karen , Mackie Ian J. , Machin Samuel J. , Cohen Hannah
Published: December 2004

An ageing population and the continuing expansion of clinical indications for coumadin therapy have increased pressure on hospital anticoagulant clinics. One solution is patient self‐testing (PST) of the international normalized ratio (INR) using capillary blood samples on point‐of‐care coagulation monitors at home. We conducted a prospective study to determine whether patients can achieve accurate INR values through PST, using the CoaguChek S (Roche Diagnostics, Lewes, UK). The main outcome measurements were: comparability of INR values obtained by PST and the hospital laboratory, patient acceptability as assessed by a questionnaire and anticoagulant control. Eighty‐four patients [53 men, 31 women; median age 59 years (range 26–83)], receiving long‐term oral anticoagulation (warfarin), were recruited from our Anticoagulation Clinic. Patients were randomized to weekly self‐testing or continuing 4‐weekly hospital laboratory monitoring of INR. Comparison of INRs (n = 234) showed no significant differences between the CoaguChek (median INR 3·02) and laboratory testing (median INR 3·07). There was excellent correlation between the two methods (r = 0·95), with 85% of CoaguChek results within 0·5 INR units of the laboratory method. On four occasions, differences of >1 unit INR were obtained, but in each case the patient's anticoagulation was unstable (INR >4·5 by both methods) and the differences in INR would not have altered patient management. 87% of patients found self‐testing straightforward, 87% were confident in the result they obtained and 77% preferred self‐testing. We conclude that PST is a reliable alternative to hospital clinic attendance and is acceptable to the majority of suitably trained patients.
Does elevated CO2 facilitate naturalization of the non‐indigenous Prunus laurocerasus in Swiss temperate forests?
Authors: Hättenschwiler S. , Körner C.
Published: December 2004

An increasing abundance of the non‐indigenous evergreen woody plant species Prunus laurocerasus has been observed in the understorey of Swiss temperate forests. We addressed the question whether rising atmospheric CO2 concentration contributes to the success of this species in a comparative test with four co‐occurring native species (Ilex aquifolium, Hedera helix, Fraxinus excelsior, Carpinus betulus).

We grew plants from germination to the end of the third growing season in open‐top chambers exposed to either ambient or two elevated CO2 concentrations (500 and 660 µmol mol−1) in a deeply shaded forest understorey (1·2–3·2% of full sun).

Species differed greatly in their response to CO2. Biomass growth in Prunus increased by an average of 56% at the two elevated CO2 concentrations compared to ambient CO2; there was no significant difference between 500 and 660 µmol mol−1. In contrast the native Ilex, with the same functional traits, a similar life history and occurring in the same habitat, showed no significant CO2 response.

A particularly large and nearly linear CO2 effect on seedling growth was observed in the liana Hedera with 100% more biomass and 137% longer stems at 660 µmol CO2 mol−1 compared to ambient CO2. Seedlings of the deciduous tree species Fraxinus produced 43% more biomass at elevated CO2 (no significant difference between 500 and 660 µmol mol−1), but there was no significant CO2 effect on Carpinus seedlings.

Our results indicate that elevated CO2 might contribute to the current spread of Prunus in natural forests. The strong CO2 response in Hedera suggests an increasing rate of tree colonization with rising CO2. Increasing dominance of non‐indigenous understorey species and accelerated liana colonization of canopy trees could both have far‐ranging consequences for forest community dynamics and composition.
Effect of ingestion by five avian dispersers on the retention time, retrieval and germination of Ruppia maritima seeds
Authors: Charalambidou I. , Santamaria L. , Langevoord O.
Published: December 2004

Vertebrates are important seed dispersers for many plants, particularly those inhabiting naturally fragmented habitats such as lakes and wetlands. Such dispersal often takes place through the transport of ingested seeds (endozoochory).

Endozoochorous passage of seeds is likely to vary among both disperser and dispersed species. We hypothesized that seed retention time and survival of gut passage varies among disperser species (here Anas ducks) and is influenced by intraspecific differences in seed size.

Wigeongrass (Ruppia maritima) seeds were ingested by five duck species; Teal, Wigeon, Shoveler, Pintail and Mallard. Defecated seeds were recovered and germinated.

Total retrieval and germination of seeds, patterns of retrieval over time and seed weight before and after gut passage did not differ among duck species. Hence interspecific differences among Anas ducks and intraspecific differences in seed weight do not affect seed retention time or the response of seeds to gut passage.

Germination of retrieved seeds was influenced by the retention time in the gut, with seeds voided earlier more likely to germinate than those voided later.

The probability of dispersal at different retention times by any given duck was low. However, when considering the thousands of ducks moving among wetlands, the dispersal probabilities of seeds become significant.

Estimation of seed dispersal distance as a function of retention time suggested higher dispersal probabilities for seeds voided earlier. Based on average flight speeds ranging from 10 to 70 km h−1, most probable dispersal distances range from 40 to 280 km. Dispersal over greater distances is possible, but less likely.
Compensatory growth following early nutritional stress in the Wolf Spider Pardosa prativaga
Authors: Jespersen L. B. , Toft S.
Published: December 2004

Spiders may often be subjected to nutritional stress during their development, either because of lack of prey (starvation) or because the prey available is nutritionally insufficient or chemically defended (i.e. deterrent or toxic). The ability of the Wolf Spider Pardosa prativaga (L. Koch) to catch up on growth and development after treatment with different types and intensities of nutritional stress in the initial period of independent life was tested.

The stress types (prey) were: (1) starvation; (2) toxicity (the collembolan Folsomia candida Willem); (3) deterrency (the aphid Rhopalosiphum padi L.); (4) nutritional insufficiency (the fruit fly Drosophila melanogaster Meigen). Nutrient‐enriched D. melanogaster was used as control and was also the food given to the treated spiders after the stress period ended.

Though the spiderlings were set back considerably, especially by starvation and toxic and deterrent prey, those that survived achieved the same weight as the control spiders within 3–7 weeks, depending on treatment. The duration of instars after termination of the stress treatment was not affected. Thus, seemingly compensation was accomplished by a burst of supernormal growth initiated shortly after the stress was alleviated.

Growth compensation is considered a physiological mechanism that allows spiders an optimal seasonal timing of the life cycle even if their phenology is retarded in its early phases.
Light‐acquisition and use of individuals as influenced by elevated CO2 in even‐aged monospecific stands of Chenopodium album
Authors: Hikosaka K. , Yamano T. , Nagashima H. , Hirose T.
Published: December 2004

We studied the effect of CO2 elevation on photosynthesis and growth of individuals in even‐aged monospecific stands of an annual, Chenopodium album, established at ambient and doubled CO2 concentrations in open‐top chambers.

The whole‐plant photosynthesis of every individual in the stand was calculated from (1) the distribution of light and leaf nitrogen and (2) the relationships between photosynthetic parameters and leaf nitrogen content per area. Elevated CO2 increased light‐saturated rates of photosynthesis by 10–15% and the initial slope of the light‐response curve by 11%, but had no effect on the convexity of the light‐response curve and dark respiration.

The relative rate of photosynthesis (RPR, the rate of photosynthesis per unit above‐ground mass) was analysed as the product of light capture (Φmass, the photon flux captured per unit above‐ground mass) and light‐use efficiency (LUE, plant photosynthesis per unit photon capture).

At an early stage of stand development (33 days after germination), RPR was nearly constant and no difference was found between ambient and elevated CO2. However, CO2 elevation influenced the components of RPR such that the reduction in Φmass at elevated CO2 offsets the effect of the higher LUE. Later (47 days), RPR was positively correlated with plant mass at both CO2 concentrations. When compared at an equal plant mass, RPR was lower at elevated CO2, which was caused by a reduction in Φmass despite some compensation by higher LUE.

We conclude that elevated CO2 increases size inequality of a stand through enhanced photosynthesis and growth of dominants, which reduce the light availability for subordinates and consequently increase size inequality in the stand.
The geographical range structure of the Holly Leaf‐miner. III. Cold hardiness physiology
Authors: Klok C. J. , Chown S. L. , Gaston K. J.
Published: December 2004

The thermal tolerances of a phytophagous insect, the Holly Leaf‐minerPhytomyza ilicisCurtis, a specialist on hollyIlex aquifoliumL., were investigated to determine whether these contribute to the high levels of miscellaneous larval mortalities that play an important role in determining the local abundances of this species across its geographical range.

Temperatures of crystallization, lower and upper lethal temperatures and rapid cold hardening experiments indicated that the Holly Leaf‐miner has a pronounced cold hardiness, exceeding that of its host plant. Acute exposure to cold does not therefore contribute directly to miscellaneous mortalities and neither do summer temperatures exceed the upper lethal limits of the larvae.

Holly Leaf‐miner densities are north‐skewed; in the south densities gradually taper off and disappear well north of the distribution limits of the host plant. The parasitoidChrysocharis gemmacauses high larval mortalities in the centre of the distribution of the Holly Leaf‐miner and is absent in the cold north, with the level of parasitism being positively correlated with miscellaneous mortalities. OnlyC. gemmaadults overwinter and the attacks on Holly Leaf‐miner, starting late winter, are likely opportunistic. This, andC. gemma's absence in the cold north, suggest significant cold susceptibility inC. gemmalarvae. Thus, the greater proportion of miscellaneous larval mortalities of the Holly Leaf‐miner are possibly the result of pre‐premature deaths whenC. gemmalarvae are killed by cold snaps in late winter.
Maternal age affects offspring lifespan of the seed beetle,Callosobruchus maculatus
Authors: Fox C. W. , Bush M. L. , Wallin W. G.
Published: December 2004

Offspring from older parents often have shorter adult lifespans than offspring of younger mothers. We examine the effects of offspring genotype, maternal age and paternal age on offspring survival, development and adult lifespan in the seed beetle,Callosobruchus maculatus.

Females took about a quarter of a day longer to develop from an egg to an adult and lived ≈7 days longer than males. Mortality patterns were best described by a logistic mortality model, and all three model parameters differed significantly between the sexes; females had a higher baseline mortality rate than males but the mortality rate increased more slowly in females than in males. Females also showed a delay, relative to males, in the age at which mortality became age‐dependent.

The proportion of eggs that hatched and larval survivorship both declined with increasing maternal age, while egg‐to‐adult development time increased substantially. Contrary to the pattern observed in many other organisms, offspring of older mothers livedlongerthan offspring of younger mothers, even after controlling for heterogeneity among families. There was no evidence that paternal age affected any offspring traits.

The effect of maternal age on offspring lifespan was greater for male offspring than for female offspring (consistent with the general observation that the genetic and environmental factors affecting lifespan differ between the two sexes) and varied among sire families (indicating that offspring genotype mediated the non‐genetic effect of maternal age on lifespan).
Egg yolk androgen levels increase with breeding density in the European Starling,Sturnus vulgaris
Authors: Pilz K. M. , Smith H. G.
Published: December 2004

High breeding density can cause elevated plasma androgen levels in adult birds. Since maternal androgens are deposited into egg yolk, high breeding density may result in elevated yolk androgen levels as well.

The relationship between breeding density and yolk androgen levels was examined in the European Starling,Sturnus vulgaris. The concentration and total content of yolk androstenedione and yolk testosterone were measured in eggs from 24 clutches distributed across nine different colonies of nestboxes.

Yolk androstenedione and testosterone levels were significantly higher in colonies where a greater proportion of nestboxes had active nests.

Yolk testosterone levels were significantly higher, and yolk androstenedione levels were marginally higher, in colonies with a greater absolute number of active nests.

Yolk androgen levels were not related to the number of active nests in adjacent nestboxes.

We conclude that female starlings nesting in colonies with higher breeding densities transfer more androgen to their eggs.

This relationship may be mediated by increased interfemale aggression, particularly towards floater females searching for mates or nests to brood parasitize, in high‐density colonies. Such a relationship between maternal environment and maternal yolk androgens may represent adaptive maternal modification of offspring phenotype or a non‐adaptive physiological constraint which females cannot avoid.
The experimental rearing of large salmonid eggs in Petri dishes
Authors: Wedekind C. , Müller R.
Published: December 2004

Studies on the genetics or the ecology of fish eggs are typically based on inferential statistics, which require the separate rearing of many batches.

Salmonid eggs are believed to require a constant water flow to develop safely. Therefore, the technical requirements that have been used to rear individual batches of salmonid eggs significantly limit experimental studies.

We describe a technique that allows, for the first time, the large eggs of Arctic Charr (Salvelinus alpinus) to be reared under experimental conditions in Petri dishes.

It was found that the proportion of well‐developed eggs on day 64 did not significantly correlate with egg density in the Petri dish, but that fry hatch earlier under more crowded conditions.

Oxygen concentration measured shortly before hatching appeared to be above critical values.
Allometric and phylogenetic variation in insect phosphorus content
Authors: Woods H. A. , Fagan W. F. , Elser J. J. , Harrison J. F.
Published: December 2004

Phosphorus content was measured in adult insects and arachnids from 170 species collected in the Sonoran Desert.

Across insect body sizes spanning four orders of magnitude, phosphorus content was inversely related to body mass. The largest species (∼1 g dry) had phosphorus contents that were only about 60% (0·62% P absolute) as high as phosphorus contents of the smallest species (∼0·0001 g dry; 0·97% P). Negative phosphorus allometry was observed within each of seven insect orders and within arachnids.

Phosphorus contents of insect predators and herbivores were statistically indistinguishable.

More recently derived orders tended to have lower phosphorus contents – with the exception of the most recently derived group (Panorpida = Diptera + Lepidoptera), which had high phosphorus contents.
Prion domain interaction responsible for species discrimination in yeast [PSI+] transmission
Authors: Hara Hideyuki , Nakayashiki Toru , Crist Colin G. , Nakamura Yoshikazu
Published: December 2004

Background:  The yeast [PSI+] factor is transmitted by a prion mechanism involving self‐propagating Sup35 aggregates. As with mammalian prions, a species barrier prevents prion transmission between yeast species. The N‐terminal of Sup35 of Saccharomyces cerevisiae, necessary for [PSI+], contains two species‐signature elements—a Gln/Asn‐rich region (residues 1–41; designated NQ) that is followed by oligopeptide repeats (designated NR).

Results:  In this study, we show that S. cerevisiae[PSI+] is transmissible through plasmid shuffling and cytoplasmic transfer to heterotypic Sup35s whose NQ is replaced with the S. cerevisiae NQ. In addition to homology, the N‐terminal location is essential for NQ mediated susceptibility to [PSI+] transmission amongst heterotypic Sup35s. In vitro, a swap of NQ of S. cerevisiae Sup35 led to cross seeding of amyloid formation.

Conclusions:  These findings suggest that NQ discriminates self from non‐self, and is sufficient to initiate [PSI+] transmission irrespective of whether NR is heterotypic. NR as well as NQ alone coalesces into existing [PSI+] aggregates, showing their independent potentials to interact with the identical sequence in the [PSI+] conformer. The role of NQ and NR in [PSI+] prion formation is discussed.
Involvement of Cdc42 and Rac small G proteins in invadopodia formation of RPMI7951 cells
Authors: Nakahara Hirokazu , Otani Tomohiro , Sasaki Takuya , Miura Yasuhiro , Takai Yoshimi , Kogo Mikihiko
Published: December 2004

Background:  Invadopodia are membrane protrusions into the extracellular matrix by aggressive tumour cells. These structures are associated with sites of matrix degradation and invasiveness of malignant tumour cells in an in vitro fibronectin degradation/invasion assay. The Rho family small G proteins, consisting of the Rho, Rac and Cdc42 subfamilies, are implicated in various cell functions, such as cell shape change, adhesion, and motility, through reorganization of the actin cytoskeleton. We studied the roles of the Rho family small G proteins in invadopodia formation.

Results:  We first demonstrated that invadopodia of RPMI7951 human melanoma cells extended into the matrix substratum on a vertical view using a laser scanning confocal microscope system. We confirmed that invadopodia were rich in actin filaments (F‐actin) and visualized clearly with F‐actin staining on a vertical view as well as on a horizontal view. We then studied the roles of Rho, Rac, and Cdc42 in invasiveness of the same cell line. In the in vitro fibronectin degradation/invasion assay, a dominant active mutant of Cdc42 enhanced dot‐like degradation, whereas a dominant active mutant of Rac enhanced diffuse‐type degradation. Furthermore, frabin, a GDP/GTP exchange protein for Cdc42 with F‐actin‐binding activity, enhanced both dot‐like and diffuse‐type degradation. However, a dominant active mutant of Rho did not affect the fibronectin degradation. Moreover, inhibition of phosphatidylinositol‐3 kinase (PI3K) disrupted the Rac and Cdc42‐dependent actin structures and blocked the fibronectin degradation.

Conclusion:  These results suggest that Cdc42 and Rac play important roles in fibronectin degradation and invasiveness in a coordinate manner through the frabin‐Cdc42/Rac‐PI3K signalling pathway.
Effective elastic properties of randomly fractured soils: 3D numerical experiments
Authors: Saenger Erik H. , Krüger Oliver S. , Shapiro Serge A.
Published: December 2004

This paper is concerned with numerical tests of several rock physical relationships. The focus is on effective velocities and scattering attenuation in 3D fractured media. We apply the so‐called rotated staggered finite‐difference grid (RSG) technique for numerical experiments. Using this modified grid, it is possible to simulate the propagation of elastic waves in a 3D medium containing cracks, pores or free surfaces without applying explicit boundary conditions and without averaging the elastic moduli. We simulate the propagation of plane waves through a set of randomly cracked 3D media. In these numerical experiments we vary the number and the distribution of cracks. The synthetic results are compared with several (most popular) theories predicting the effective elastic properties of fractured materials. We find that, for randomly distributed and randomly orientated non‐intersecting thin penny‐shaped dry cracks, the numerical simulations of P‐ and S‐wave velocities are in good agreement with the predictions of the self‐consistent approximation. We observe similar results for fluid‐filled cracks. The standard Gassmann equation cannot be applied to our 3D fractured media, although we have very low porosity in our models. This is explained by the absence of a connected porosity. There is only a slight difference in effective velocities between the cases of intersecting and non‐intersecting cracks. This can be clearly demonstrated up to a crack density that is close to the connectivity percolation threshold. For crack densities beyond this threshold, we observe that the differential effective‐medium (DEM) theory gives the best fit with numerical results for intersecting cracks. Additionally, it is shown that the scattering attenuation coefficient (of the mean field) predicted by the classical Hudson approach is in excellent agreement with our numerical results.
Euler deconvolution of the analytic signal and its application to magnetic interpretation
Authors: Keating P. , Pilkington M.
Published: December 2004

Euler deconvolution and the analytic signal are both used for semi‐automatic interpretation of magnetic data. They are used mostly to delineate contacts and obtain rapid source depth estimates. For Euler deconvolution, the quality of the depth estimation depends mainly on the choice of the proper structural index, which is a function of the geometry of the causative bodies. Euler deconvolution applies only to functions that are homogeneous. This is the case for the magnetic field due to contacts, thin dikes and poles. Fortunately, many complex geological structures can be approximated by these simple geometries. In practice, the Euler equation is also solved for a background regional field. For the analytic signal, the model used is generally a contact, although other models, such as a thin dike, can be considered. It can be shown that if a function is homogeneous, its analytic signal is also homogeneous. Deconvolution of the analytic signal is then equivalent to Euler deconvolution of the magnetic field with a background field. However, computation of the analytic signal effectively removes the background field from the data. Consequently, it is possible to solve for both the source location and structural index. Once these parameters are determined, the local dip and the susceptibility contrast can be determined from relationships between the analytic signal and the orthogonal gradients of the magnetic field. The major advantage of this technique is that it allows the automatic identification of the type of source. Implementation of this approach is demonstrated for recent high‐resolution survey data from an Archean granite‐greenstone terrane in northern Ontario, Canada.
Δx≠Δy in 3D depth migration via McClellan transformations
Authors: Levin Stewart A.
Published: December 2004

An intuitive method is presented for extending Hale–McClellan migration operators to handle surveys binned and stacked with in‐line and cross‐line spacings unequal. This avoids re‐interpolating the input to 3D migration, either externally or internally. The algorithm does not require an integer or rational ratio between the in‐line and cross‐line spacings in order to be applied nor does it deliberately introduce artificial aliasing by interleaving subsampled grids along the more finely sampled axis. Examples of its impulse response and application to the SEG–EAGE salt model are shown.
An accurate and robust multigrid algorithm for 2D forward resistivity modelling
Authors: Moucha Robert , Bailey Richard C.
Published: December 2004

We present an adaptation of the full multigrid algorithm in DC resistivity modelling in an effort to increase its accuracy. There is a great difficulty with conventional multigrid solvers in representing the physics of an arbitrary distribution of electrical conductivity on a very coarse grid. In general, conventional rectangular finite‐difference or 5‐point approximations of Poisson's equation cannot represent, at a coarse grid level, the effective anisotropy on a coarse scale which results from fine structure in the model. An exception to this generalization occurs when the principal axes of structural anisotropy are aligned with the coordinate axis. Additional and similarly generated problems arise when a coarse cell is obliged to represent fine structure containing very high conductivity contrasts. We have developed an adaptation of the usual resistive‐network representation of the continuum, which avoids some of these problems, and have compared it with the traditional resistive network currently used. The network adaptation consists of replacing the usual 5‐point Laplacian operator stencil used on the finite‐difference grid with a 9‐point stencil, and the conductivity scalar with a 6‐parameter conductivity parametrization. This parametrization permits representation of arbitrarily orientated anisotropy as well as more complex behaviour related to high conductivity contrasts. The importance of multigrid solvers does not lie in their speed at forward modelling (which is comparable with other methods), but rather in their potential for inverse modelling. Inverse solvers which proceed by refinement of an initially very coarse solution can, in principle, take time only linearly proportional to the number of gridpoints in the final desired model.
Adjustment of regularization in ill‐posed linear inverse problems by the empirical Bayes approach
Authors: Mitsuhata Yuji
Published: December 2004

Regularization is the most popular technique to overcome the null space of model parameters in geophysical inverse problems, and is implemented by including a constraint term as well as the data‐misfit term in the objective function being minimized. The weighting of the constraint term relative to the data‐fitting term is controlled by a regularization parameter, and its adjustment to obtain the best model has received much attention. The empirical Bayes approach discussed in this paper determines the optimum value of the regularization parameter from a given data set. The regularization term can be regarded as representing a priori information about the model parameters. The empirical Bayes approach and its more practical variant, Akaike's Bayesian Information Criterion, adjust the regularization parameter automatically in response to the level of data noise and to the suitability of the assumed a priori model information for the given data. When the noise level is high, the regularization parameter is made large, which means that the a priori information is emphasized. If the assumed a priori information is not suitable for the given data, the regularization parameter is made small. Both these behaviours are desirable characteristics for the regularized solutions of practical inverse problems. Four simple examples are presented to illustrate these characteristics for an underdetermined problem, a problem adopting an improper prior constraint and a problem having an unknown data variance, all frequently encountered geophysical inverse problems. Numerical experiments using Akaike's Bayesian Information Criterion for synthetic data provide results consistent with these characteristics. In addition, concerning the selection of an appropriate type of a priori model information, a comparison between four types of difference‐operator model – the zeroth‐, first‐, second‐ and third‐order difference‐operator models – suggests that the automatic determination of the optimum regularization parameter becomes more difficult with increasing order of the difference operators. Accordingly, taking the effect of data noise into account, it is better to employ the lower‐order difference‐operator models for inversions of noisy data.
Interpretation of magnetic data using analytic signal derivatives
Authors: Salem Ahmed
Published: December 2004

This paper develops an automatic method for interpretation of magnetic data using derivatives of the analytic signal. A linear equation is derived to provide source location parameters of a 2D magnetic body without a priori information about the nature of the source. Then using the source location parameters, the nature of the source can be ascertained. The method has been tested using theoretical simulations with random noise for two 2D magnetic models placed at different depths with respect to the observation height. In both cases, the method gave a good estimate for the location and shape of the sources. Good results were obtained on two field data sets.
Dense 3D residual moveout analysis as a tool for HTI parameter estimation
Authors: Kozlov Evgenii A. , Varivoda Dmitry Y.
Published: December 2004

Three‐dimensional residual moveout analysis is the basic step in velocity model refinement. The analysis is generally carried out using horizontal and/or vertical semblances defined on a sparse set of in‐lines or cross‐lines with densely sampled source–receiver offsets. An alternative approach, which we call dense residual moveout analysis (DRMA), is to use all the bins of a three‐dimensional survey but sparsely sampled offsets. The proposed technique is very fast and provides unbiased and statistically efficient estimates of the residual moveout. Indeed, for the sparsest possible offset distribution, when only near‐ and far‐angle stacks are used, the variance of the residual moveout estimate is only 1.4 times larger than the variance of the least‐squares estimate obtained using all offsets.

The high performance of DRMA makes it a useful tool for many applications, of which azimuthal velocity analysis is considered here. For a horizontal transverse isotropy (HTI) model, a deterministic procedure is proposed to define, at every point of residual moveout estimation, the azimuthal angle of the HTI axis of symmetry, the Thomsen anisotropy coefficients, and the interval (or root‐mean‐square) velocities in both the HTI isotropy and symmetry planes. The procedure is not restricted by DRMA assumptions; for example, it is also applicable to semblance‐based residual moveout estimates.

The high resolution of the technique is illustrated by azimuthal velocity analysis over an oilfield in West Siberia.
Effects of elevated atmospheric CO2 on net ecosystem CO2 exchange of a scrub–oak ecosystem
Authors: Hymus Graham J. , Johnson David P. , Dore Sabina , Anderson Hans P. , Ross Hinkle C. , Drake Bert G.
Published: December 2004

We report the results of a 2‐year study of effects of the elevated (current ambient plus 350 μmol CO2 mol−1) atmospheric CO2 concentration (Ca) on net ecosystem CO2 exchange (NEE) of a scrub–oak ecosystem. The measurements were made in open‐top chambers (OTCs) modified to function as open gas‐exchange systems. The OTCs enclosed samples of the ecosystem (ca. 10 m2 surface area) that had regenerated after a fire, 5 years before, in either current ambient or elevated Ca. Throughout the study, elevated Ca increased maximum NEE (NEEmax) and the apparent quantum yield of the NEE (φNEE) during the photoperiod. The magnitude of the stimulation of NEEmax, expressed per unit ground area, was seasonal, rising from 50% in the winter to 180% in the summer. The key to this stimulation was effects of elevated Ca, and their interaction with the seasonal changes in the environment, on ecosystem leaf area index, photosynthesis and respiration. The separation of these factors was difficult. When expressed per unit leaf area the stimulation of the NEEmax ranged from 7% to 60%, with the increase being dependent on increasing soil water content (Wsoil). At night, the CO2 effluxes from the ecosystem (NEEnight) were on an average 39% higher in elevated Ca. However, the increase varied between 6% and 64%, and had no clear seasonality. The partitioning of NEEnight into its belowground (Rbelow) and aboveground (Rabove) components was carried out in the winter only. A 35% and 27% stimulation of NEEnight in December 1999 and 2000, respectively, was largely due to a 26% and 28% stimulation of Rbelow in the respective periods, because Rbelow constituted ca. 87% of NEEnight. The 37% and 42% stimulation of Rabove in December 1999 and 2000, respectively, was less than the 65% and 80% stimulation of the aboveground biomass by elevated Ca at these times. An increase in the relative amount of the aboveground biomass in woody tissue, combined with a decrease in the specific rate of stem respiration of the dominant species Quercus myrtifolia in elevated Ca, was responsible for this effect. Throughout this study, elevated Ca had a greater effect on carbon uptake than on carbon loss, in terms of both the absolute flux and relative stimulation. Consequently, for this scrub–oak ecosystem carbon sequestration was greater in the elevated Ca during this 2‐year study period.
Photosynthetic and gas exchange characteristics of dominant woody plants on a moisture gradient in an African savanna
Authors: Midgley Guy Franklin , Aranibar Julieta Nelida , Mantlana Khanyisa Brian , Macko Stephen
Published: December 2004

We determined key photosynthetic gas exchange parameters, and their temperature dependence, in dominant woody plants at four savanna sites on a moisture gradient in Botswana, southern Africa. Leaf stable carbon and nitrogen (N) isotope and morphological measures were made concurrently. Sampling of these predominantly non‐N‐fixing species took place during an exceptional rainfall season, representing near‐optimum conditions for primary production at these sites. The mean specific leaf area and leaf size were positively related to mean annual rainfall (MAR); species with larger leaves of lower density were more abundant in wetter sites. Almost all species at all sites showed high net light‐saturated photosynthetic rates (Amax≫10 μmol CO2 m−2 s−1) due both to high CO2 carboxylation (Vc,max) and RubP‐regeneration capacity (Jmax). These high rates were associated with high values of leaf [N]. Across all sites, the temperature response of Amax showed no clear optimum, and a gradual drop from 25°C to 35°C, without notable temperature limitation at leaf temperatures in excess of 35°C. Dark respiration rate (Rday) across all species and sites increased exponentially with increasing leaf temperature. Species sampled at selected sites revealed a negative relationship between leaf δ13C (stable carbon isotope ratio) and MAR, suggesting higher leaf‐level water‐use efficiency at drier sites when integrated over the life of the leaf. At wetter sites, specific leaf [N] was lower and photosynthetic nitrogen‐use efficiency increased, a pattern reflected at the ecosystem level by less 15N enrichment of leaves at these sites. Taken together, the results suggest a switch from water‐use to nitrogen‐use efficiency constraints with increasing moisture availability. These constraints impact leaf form and function significantly, and may emerge at the ecosystem level in aspects of water and N cycling.
Nitrogen cycling in the soil–plant system along a precipitation gradient in the Kalahari sands
Authors: Aranibar Julieta N. , Otter Luanne , Macko Stephen A. , Feral Chris J. W. , Epstein Howard E. , Dowty Peter R. , Eckardt Frank , Shugart Herman H. , Swap Robert J.
Published: December 2004

Nitrogen (N) cycling was analyzed in the Kalahari region of southern Africa, where a strong precipitation gradient (from 978 to 230 mm mean annual precipitation) is the main variable affecting vegetation. The region is underlain by a homogeneous soil substrate, the Kalahari sands, and provides the opportunity to analyze climate effects on nutrient cycling. Soil and plant N pools, 15N natural abundance (δ15N), and soil NO emissions were measured to indicate patterns of N cycling along a precipitation gradient. The importance of biogenic N2 fixation associated with vascular plants was estimated with foliar δ15N and the basal area of leguminous plants. Soil and plant N was more 15N enriched in arid than in humid areas, and the relation was steeper in samples collected during wet than during dry years. This indicates a strong effect of annual precipitation variability on N cycling. Soil organic carbon and C/N decreased with aridity, and soil N was influenced by plant functional types. Biogenic N2 fixation associated with vascular plants was more important in humid areas. Nitrogen fixation associated with trees and shrubs was almost absent in arid areas, even though Mimosoideae species dominate. Soil NO emissions increased with temperature and moisture and were therefore estimated to be lower in drier areas. The isotopic pattern observed in the Kalahari (15N enrichment with aridity) agrees with the lower soil organic matter, soil C/N, and N2 fixation found in arid areas. However, the estimated NO emissions would cause an opposite pattern in δ15N, suggesting that other processes, such as internal recycling and ammonia volatilization, may also affect isotopic signatures. This study indicates that spatial, and mainly temporal, variability of precipitation play a key role on N cycling and isotopic signatures in the soil–plant system.
Seasonal variation in energy fluxes and carbon dioxide exchange for a broad‐leaved semi‐arid savanna (Mopane woodland) in Southern Africa
Authors: Veenendaal Elmar M. , Kolle Olaf , Lloyd Jon
Published: December 2004

We studied the seasonal variation in carbon dioxide, water vapour and energy fluxes in a broad‐leafed semi‐arid savanna in Southern Africa using the eddy covariance technique. The open woodland studied consisted of an overstorey dominated by Colophospermum mopane with a sparse understorey of grasses and herbs. Measurements presented here cover a 19‐month period from the end of the rainy season in March 1999 to the end of the dry season September 2000.

During the wet season, sensible and latent heat fluxes showed a linear dependence on incoming solar radiation (I) with a Bowen ratio (β) typically just below unity. Although β was typically around 1 at low incoming solar radiation (150 W m−2) during the dry season, it increased dramatically with I, typically being as high as 4 or 5 around solar noon. Thus, under these water‐limited conditions, almost all available energy was dissipated as sensible, rather than latent heat.

Marked spikes of CO2 release occurred at the onset of the rainfall season after isolated rainfall events and respiration dominated the balance well into the rainfall season. During this time, the ecosystem was a constant source of CO2 with an average flux of 3–5 μmol m−2 s−1 to the atmosphere during both day and night. But later in the wet season, for example, in March 2000 under optimal soil moisture conditions, with maximum leaf canopy development (leaf area index 0.9–1.3), the peak ecosystem CO2 influx was as much as 10 μmol m−2 s−1. The net ecosystem maximum photosynthesis at this time was estimated at 14 μmol m−2 s−1, with the woodland ecosystem a significant sink for CO2. During the dry season, just before leaf fall in August, maximum day‐ and night‐time net ecosystem fluxes were typically −3 μmol m−2 s−1 and 1–2 μmol m−2 s−1, respectively, with the ecosystem still being a marginal sink.

Over the course of 12 months (March 1999–March 2000), the woodland was more or less carbon neutral, with a net uptake estimated at only about 1 mol C m−2 yr−1. The annual net photosynthesis (gross primary production) was estimated at 32.2 mol m−2 yr−1.