bluuebunny/crossref_metadata_2025 huggingface dataset:
Photodissociation of HCl and small (HCl)m complexes in and on large Arn clusters
Authors: Nahler N. Hendrik , Fárnı́k Michal , Buck Udo , Vach Holger , Gerber R. Benny
Published: July 2004

Photodissociation experiments were carried out at 193 nm for single HCl molecules which are adsorbed on the surface of large Arn clusters and small (HCl)m complexes which are embedded in the interior of these clusters. For the surface case the size dependence is measured for the average sizes 〈n〉=140–1000. No cage exit events are observed in agreement with the substitutional position of the molecule deeply buried in the outermost shell. This result is confirmed by a molecular dynamics simulation of the pickup process under realistic conditions concerning the experiment and the interaction potentials. The calculations of the dissociation process employ the surface hopping model. For the embedded case the average sizes covered are 〈m〉=3 and 6 and 〈n〉=8–248. The kinetic energy of the H atom fragments is measured exhibiting peaks at zero and around 2.0 eV which mark completely caged and unperturbed fragments, respectively. The ratio of theses peaks strongly depends on the cluster size and agrees well with theoretical predictions for one and two closed icosahedral shells, in which the nonadiabatic coupling of all states was accounted for.
Nucleation kinetics of folded chain crystals of polyethylene on active centers
Authors: Kožı́šek Zdeněk , Hikosaka Masamichi , Demo Pavel , Sveshnikov Alexei M.
Published: July 2004

Kinetic equations describing formation of nuclei of a new phase on active centers from supercooled melt taking into account exhaustion of active centers are solved numerically. Basic characteristics of nucleation process (total number of nuclei and nucleation rate) of folded chain crystals of polyethylene at low supercooling are determined and compared with measured data. Our model gives good coincidence with experimental measurements of the total number density of nuclei. Nucleation rate reaches some quasistationary limit at sufficiently long time, which is approximately 20% of the stationary nucleation rate determined by the standard way.
Singular value decomposition applied to the compression of T3 amplitude for the coupled cluster method
Authors: Hino Osamu , Kinoshita Tomoko , Bartlett Rodney J.
Published: July 2004

We apply the singular value decomposition to compress the degrees of freedom of T3 amplitude for the CCSDT-1 method (compressed CCSDT-1). This method enables us to make the number of the T3 amplitudes less than that of the T2 amplitudes, making CCSDT-1 calculations much less expensive without losing accuracy. We perform test calculations on some atoms and molecules to investigate the applicability of this method. Computational results for the electronic energies as well as timings of these calculations are presented.
Theoretical study of the reaction of acrylonitrile on Si(001)
Authors: Cho Jun-Hyung , Kleinman Leonard
Published: July 2004

Two recent experiments for adsorbed acrylonitrile on the Si(001) surface reported different adsorption structures at 110 and 300 K. We investigate the reaction of acrylonitrile on Si(001) by first-principles density-functional calculations. We find that the so-called [4+2] structure in which acrylonitrile resides between two dimer rows is not only thermodynamically favored over other structural models but also easily formed via a precursor where the N atom of acrylonitrile is attached to the down atom of the Si dimer. The additional initial-state theory calculation for the C 1s core levels of adsorbed acrylonitrile provides an interpretation for the observed low- and room-temperature adsorption configurations in terms of the precursor and [4+2] structures, respectively.
Dynamical origin of enhanced conformational searches of Tsallis statistics sampling
Authors: Kim Jae Gil , Fukunishi Yoshifumi , Nakamura Haruki
Published: July 2004

The characteristic sampling dynamics of importance samplings driven by the Tsallis weight [C. Tsallis, J. Stat. Phys. 52, 479 (1988)] has been analyzed in terms of recently developed Langevin stochastic model by considering the effects of the density of states and the potential smoothing of the Tsallis transformation. Our study reveals that the fixed points, which are determined by the crossing points of the statistical temperature and the Tsallis effective temperature, play a critical role in overall dynamics of the Tsallis statistics sampling. The dynamical origin of enhanced conformational searches of the Tsallis weight has been investigated by unveiling the intimate relationship between the sampling dynamics and the stability change of corresponding fixed points. Based on this stochastic analysis, we propose one effective method to realize a broad energy distribution in the Tsallis statistics sampling by determining optimal Tsallis parameters systematically based on preliminary canonical samplings. The effectiveness of our method has been validated in the folding simulation of Met-Enkephalin and liquid-solid transition simulation of Lennard-Jones cluster systems.
Lifetimes of cagelike water clusters immersed in bulk liquid water: A molecular dynamics study on gas hydrate nucleation mechanisms
Authors: Guo Guang-Jun , Zhang Yi-Gang , Zhao Ya-Juan , Refson Keith , Shan Gui-Hua
Published: July 2004

Molecular dynamics simulations were performed to observe the evolution of cagelike water clusters immersed in bulk liquid water at 250 and 230 K. Totally, we considered four types of clusters—dodecahedral (512) and tetrakaidecahedral (51262) cagelike water clusters filled with or without a methane molecule, respectively. The lifetimes of these clusters were calculated according to their Lindemann index (δ) using the criterion of δ⩾0.07. The lifetimes of the clusters at 230 K are longer than that at 250 K, and their ratios are the same as the ratio of structure relaxation times of bulk water at these temperatures. For both the filled and empty clusters, the lifetimes of 51262 cagelike clusters are similar to that of 512 cagelike clusters. Although the methane molecules indeed make the filled cagelike water clusters live longer than the empty ones, the empty cagelike water clusters still have the chance of being long lived. These observations support the cluster nucleation hypothesis for the formation mechanisms of gas hydrates.
LocalSCF method for semiempirical quantum-chemical calculation of ultralarge biomolecules
Authors: Anikin N. A. , Anisimov V. M. , Bugaenko V. L. , Bobrikov V. V. , Andreyev A. M.
Published: July 2004

A linear-scaling semiempirical method, LocalSCF, has been proposed for the quantum-chemical calculations of ultralarge molecular systems by treating the large-scale molecular task as a variational problem. The method resolves the self-consistent field task through the finite atomic expansion of weakly nonorthogonal localized molecular orbitals. The inverse overlap matrix arising from the nonorthogonality of the localized orbitals is approximated by preserving the first-order perturbation term and applying the second-order correction by means of a penalty function. This allows for the separation of the orbital expansion procedure from the self-consistent field optimization of linear coefficients, thereby maintaining the localized molecular orbital size unchanged during the refinement of linear coefficients. Orbital normalization is preserved analytically by the variation of virtual degrees of freedom, which are orthogonal to the initial orbitals. Optimization of linear coefficients of localized orbitals is performed by a gradient procedure. The computer program running on a commodity personal computer was applied to the GroEL-GroES chaperonin complex containing 119 273 atoms.
Ab initio vibrational state calculations with a quartic force field: Applications to H2CO, C2H4, CH3OH, CH3CCH, and C6H6
Authors: Yagi Kiyoshi , Hirao Kimihiko , Taketsugu Tetsuya , Schmidt Michael W. , Gordon Mark S.
Published: July 2004

For polyatomic molecules, n-mode coupling representations of the quartic force field (nMR-QFF) are presented, which include terms up to n normal coordinate couplings in a fourth-order polynomial potential energy function. The computational scheme to evaluate third-and fourth-order derivatives by finite differentiations of the energy is fully described. The code to generate the nMR-QFF has been implemented into GAMESS program package and interfaced with the vibrational self-consistent field (VSCF) and correlation corrected VSCF (cc-VSCF) methods. As a demonstration, fundamental frequencies have been calculated by the cc-VSCF method based on 2MR-QFF for formaldehyde, ethylene, methanol, propyne, and benzene. The applications show that 2MR-QFF is a highly accurate potential energy function, with errors of 1.0–1.9% relative to the experimental value in fundamental frequencies. This approach will help quantitative evaluations of vibrational energies of a general molecule with a reasonable computational cost.
A consistent integral equation theory for hard spheres
Authors: Bomont Jean-Marc , Bretonnet Jean-Louis
Published: July 2004

The standard integral equation approach is used to extract the bridge function and other correlation functions of hard spheres fluid. To achieve this, we first use a recent consistent closure relation proposed by Bomont et al. [J. Chem. Phys. 119, 2188 (2003)] that has already proven to be accurate to describe the Lennard-Jones fluid properties. Second, we take advantage of the coherent scheme derived by Bomont [J. Chem. Phys. 119, 11484 (2003)] to calculate the excess chemical potential, the entropy and some relative transport properties. Very good agreement is obtained for structural quantities and thermodynamic properties as compared to exact data at densities ranging from 0.1 to 0.9.
Mapping potential energy surfaces
Authors: Wu Yudong , Schmitt Jeffrey D. , Car Roberto
Published: July 2004

A recently proposed dynamical method [A. Laio and M. Parrinello, Proc. Natl. Acad. Sci. U.S.A. 99, 12562 (2002)] allows us to globally sample the free energy surface. This approach uses a coarse-grained non-Markovian dynamics to bias microscopic atomic trajectories. After a sufficiently long simulation time, the global free energy surface can be reconstructed from the non-Markovian dynamics. Here we apply this scheme to study the T=0 free energy surface, i.e., the potential energy surface in coarse-grained space. We show that the accuracy of the reconstructed potential energy surface can be dramatically improved by a simple postprocessing procedure with only minor computational overhead. We illustrate this approach by conducting conformational analysis on a small organic molecule, demonstrating its superiority over traditional unbiased approaches in sampling potential energy surfaces in coarse-grained space.
The Preparation of 1,2-Bis(2,2′:6′,2′′-Terpyridin-4′yl)Ethanone: The First Example of 4′-Terpyridyls Unsymmetrically Linked by a Functionalized Two-Carbon Chain
Authors: Chen Zhi-Long , Warrener Ronald N. , Butler Douglas N.
Published: July 2004

1,2-Bis(2,2′:6′,2′′-terpyridin-4′yl)ethanone 7, an unsymmetrically linked bis-tridentatate ligand, was prepared by treatment of 4′-cyanomethylterpyridine 10 (RT, overnight) or 4′-(methoxycarbonylmethyl)terpyridine 11 (60°C, 7 h) with concentrated hydrochloric acid. These conversions, which involved an unprecedented homo-coupling reaction, are discussed with the structure of 7 being confirmed by X-ray single crystal analysis. The nitrile starting material 10 was prepared by reaction of the mesylate 9, derived from the known 4′-hydroxymethylterpyridine 8 with sodium cyanide, while ester 11 was prepared by reaction of 10 with methanol in the presence of concentrated sulfuric acid.
Highly Diastereoselective Radical Reactions of Substituted Methylideneimidazolidinones and Related Systems
Authors: Adamson George A. , Beckwith Athelstan L. J. , Chai Christina L. L.
Published: July 2004

Stannane-mediated radical addition to methylideneimidazolidinones occurs with good to excellent diastereo-selectivity. The stereochemical outcome of addition is highly dependent on the nature of the N1 substituent on the imidazolidinone ring.
State of the art in the production of transgenic goats
Authors: Baldassarre H. , Wang B. , Keefer C. L. , Lazaris A. , Karatzas C. N.
Published: July 2004

This review summarises recent advances in the field of transgenic goats for the purpose of producing recombinant proteins in their milk. Production of transgenic goats via pronuclear microinjection of DNA expression vectors has been the traditional method, but this results in low efficiencies. Somatic cell nuclear transfer has dramatically improved efficiencies in rates of transgenesis. Characterisation of transfected cells in vitro before use in nuclear transfer guarantees that kids born are transgenic and of predetermined gender. Using these platform technologies, several recombinant proteins of commercial interest have been produced, although none of them has yet gained marketing approval. Before these technologies are implemented in goat improvement programmes, efficiencies must be improved, costs reduced, and regulatory approval obtained for the marketing of food products derived from such animals.
State-of-the-art production, conservation and transfer of in-vitro-produced embryos in small ruminants
Authors: Cognié Yves , Poulin Nati , Locatelli Yann , Mermillod Pascal
Published: July 2004

Today, although not efficient enough to replace multiple ovulation and embryo transfer, in vitro embryo production for small ruminants is a platform for new reproductive technologies, such as embryo sexing, transgenesis and cloning. The in vitro embryo-production system developed for sheep and goats is more efficient now than 15 years ago, but could still be improved. Laparoscopic collection of oocytes in live animals treated with gonadotrophin indicates a promising future for the application of this technology to genetic improvement programmes. Oocyte maturation in defined medium with epidermal growth factor and cysteamine appears as efficient as oocyte maturation in follicular fluid-supplemented medium and allows future study of the effect of other factors involved in the cytoplasmic maturation of oocytes from these species. Further efforts have to be made to standardise the semen-capacitating process and to improve the quality and freezability of in-vitro-produced (IVP) embryos. The optimisation of IVP procedures for deer species has required the study of the seasonal variation of oocyte competence and the development of a specific methodology to allow the culture of embryos up to the blastocyst stage.
Hormonal treatments for the synchronisation of oestrus in dairy goats raised in the tropics
Authors: Freitas V. J. F. , Rondina D. , Júnior E. S. Lopes , Teixeira D. I. A. , Paula N. R. O.
Published: July 2004

In tropical areas, local goats are often reported as being able to reproduce throughout the year, whereas an influence of season is found to be a factor when importing different dairy breeds. In these areas, oestrus synchronisation in goats is of interest for both technical (synchronisation of kidding, adjustment to forage availability or to continuous milk supply) and genetic reasons (dissemination of improved genotypes by AI). The use of a progestagen vaginal sponge combined with equine chorionic gonadotrophin (eCG)-cloprostenol injections remains an efficient tool to achieve synchronisation in temperate and tropical zones. However, the oestrus synchronisation treatments currently used for goats in tropical regions were originally developed for goats bred in temperate regions. For this reason, several alternative possibilities for improving the efficiency of the hormonal treatment are evaluated. Oestrus synchronisation with luteolytic agents is efficient (resulting in more than 70% of goats in oestrus) and it takes into account female cyclicity. In developing regions of the tropics, the use of buck teasing appears to be a promising approach to control oestrus and ovulation. The use of this technique provides 60% of females in oestrus within 5 days of introducing the bucks. Considering the availability of nutrients as the ultimate regulator of reproduction in the tropics, the control of nutritional condition is essential before the use of hormonal treatments for oestrus synchronisation in goats bred in these regions takes place.
Preservation and artificial insemination of sexed semen in sheep
Authors: Evans G. , Hollinshead F. K. , Maxwell W. M. C.
Published: July 2004

Sperm-sexing technology using flow cytometry is in advanced stages of development for the sperm of several species. The sorting process could compromise sperm viability and sperm require specific handling procedures both before and after sorting to maintain the integrity and function of the sorted sperm. Standard freezing protocols have been modified for post-sorting cryopreservation of sperm and frozen sperm have been successfully thawed, sorted, refrozen and subsequently used to produce offspring. The relatively low numbers of available sorted sperm have, in some cases, led to modification of artificial insemination techniques to maximise efficiency of use. Multiple ovulation and embryo transfer, or in vitro fertilisation and associated technology, may lead to the more efficient use of sexed sperm.
Multiple factors affecting the efficiency of multiple ovulation and embryo transfer in sheep and goats
Authors: Gonz´lez-Bulnes Antonio , Baird David T. , Campbell Bruce K. , Cocero María J. , García-García Rosa M. , Inskeep E. Keith , López-Sebastián Antonio , McNeilly Alan S. , Santiago-Moreno Julián , Souza Carlos J.H. , Veiga-López Almudena
Published: July 2004

This review offers an overview of the basic characteristics of in vivo embryo technologies, their current status, the main findings and the advances gained in recent years, and the outstanding subjects for increasing their efficiency. The use of superovulation and embryo transfer procedures remains affected by a high variability in the ovulatory response to hormonal treatment and by a low and variable number of transferable embryos and offspring obtained. This variability has been classically identified with both extrinsic (source, purity of gonadotrophins and protocol of administration) and intrinsic factors (breed, age, nutrition and reproductive status), which are reviewed in this paper. However, emerging data indicate that the main causes of variability are related to endocrine and ovarian factors, and so the number of studies and procedures addressing a better understanding and control of these factors may be increased in the future. The accomplishment of this objective, the improvement of procedures for embryo conservation and for the selection and management of recipient females, will allow further development and application of this technology.
Preservation and evaluation of semen for artificial insemination
Authors: Gillan Lindsay , Maxwell W. M. Chis , Evans Gareth
Published: July 2004

Many years of research have been devoted to improving the fertility of preserved semen of small ruminants. There have been few significant advances in preservation in recent times, but considerable knowledge has been gained on the effect of preservation on the structure and function of spermatozoa. It has become evident that preservation greatly affects many sperm attributes, such as motility, respiratory activity, membrane status and DNA quality. Consequently, viability is reduced, transport in the female reproductive tract is inhibited, the timing of fertilisation is altered and embryo development is affected following insemination of preserved, compared to fresh spermatozoa. A greater understanding of their functional condition may lead to the development of methods of preventing these alterations or to improved methods of using the preserved spermatozoa for artificial insemination in their altered state.
Nutritional and environmental effects on reproduction in small ruminants
Authors: Martin G. B. , Rodger J. , Blache D.
Published: July 2004

Animals live in environments that are both complex and continually changing, so they have to respond to short- and long-term variations in a wide range of factors, such as photoperiod, nutrition and sociosexual signals. Before they were domesticated, animals developed reproductive strategies that coped with these changes and often took advantage of them. The physiological processes that implement these strategies have been modified to some extent during several millennia of controlled breeding, but most persist. Thus, many genotypes still exhibit profound responses to external inputs, such as the induction of ovulation by sociosexual signals and the doubling of litter size by a change in nutrition. The complexity in these responses is now becoming clearer. For example, with sociosexual signals, we now need to consider the stimulatory effects of males on females, of females on males and of females on females. Similarly, the impact of nutrition has been extended beyond the control of puberty and the production of gametes to include phenomena such as ‘fetal programming’, with its potentially profound effects on the life-long performance of the animals. Fortunately, our capacity to research these phenomena has been greatly enhanced by technical improvements in hormone assays, molecular and cellular biology, and real-time ultrasound. This has brought us a better understanding of several of the environmental influences on reproduction, including: the cellular processes within ovarian follicles that mediate the effect of nutrition on ovulation rate; the neuroendocrine pathways through which nutritional inputs affect the brain centres that control appetite and reproduction; and the intracerebral pathways through which sociosexual signals (olfactory and non-olfactory) stimulate the reproductive axis. Importantly, we are now beginning to realise that, as well as considering interactions between environmental inputs and genotype, we need to take into account interactions between the environmental factors themselves, just as the animals do. We still have a long way to go for a complete understanding, but we are nevertheless in a position where we can begin to use this information to develop new management systems for our animals to improve their productivity.
The role of sex steroid receptors in sheep female reproductive physiology
Authors: Meikle A. , Tasende C. , Sosa C. , Garófalo E. G.
Published: July 2004

Cell responsiveness to steroid hormones is related to the number and affinity of its receptors, thus factors affecting steroid expression will influence tissue sensitivity and functionality. The present review discusses the role of oestrogen and progesterone receptors in sheep female reproductive physiology. The mechanism of steroid hormone action in the target cell is introduced first; the tissue distribution, physiological functions and regulation of oestrogen receptor subtypes and progesterone receptor isoforms in ruminants are reported. The role of steroid receptors in target tissues (with emphasis on the uterus and pituitary gland) during different physiological events is addressed in an attempt to clarify oestrogen and progesterone actions in different developmental and reproductive stages: prepubertal period, oestrous cycle, pregnancy, post-partum period and seasonal anoestrus. The present review shows how the distinct reproductive stages are accompanied by dramatic changes in uterine receptor expression. The role of oestrogen and progesterone receptors in the molecular mechanism responsible for premature luteolysis that results in subnormal luteal function is discussed. Finally, the effect of nutrition on sex steroid receptor expression and the involvement on reproductive performance is reported.
Mechanisms of action of the principal prolific genes and their application to sheep production
Authors: Souza C. J. H. , González-Bulnes A. , Campbell B. K. , McNeilly A. S. , Baird D. T.
Published: July 2004

The prolificacy variation in sheep makes it an excellent animal model to understand the mechanisms regulating ovulation rate. Identification of mutations responsible for the increased prolificacy of the Inverdale, Booroola, Javanese, Cambridge and Belclare sheep open new avenues of investigation for the paracrine control of folliculogenesis. To date, all known mutations are in genes from ligands or receptors of the transforming growth factor β superfamily, and point to the bone morphogenetic protein family of peptides as local regulators of ovarian follicle growth. The mechanism of action of the mutated genes is not fully understood, but results in the ovulation of a higher number of follicles with smaller diameter and fewer granulosa cells than that of the wildtype, thus speeding the differentiation of ovulatory follicles. Comparisons of the performance of Booroola-crossed flocks in different countries showed that carriers of the prolificacy mutation have higher ewe productivity but also higher perinatal mortality and lighter weight lambs. Their economic impact on the sheep industry depends on farm environment and management. Nevertheless, the diagnostic tests now available to identify the genetic mutations resulting in increased ovulation rate, will simplify the introduction of these mutations and their monitoring in flocks for research and commercial purposes.
Loss of T-bet, But Not STAT1, Prevents the Development of Experimental Autoimmune Encephalomyelitis
Authors: Bettelli Estelle , Sullivan Brandon , Szabo Susanne J. , Sobel Raymond A. , Glimcher Laurie H. , Kuchroo Vijay K.
Published: July 2004

The transcription factors signal transducer and activator of transcription (STAT)1 and T-bet control the differentiation of interferon (IFN)-γ–producing T helper type (Th)1 cells. Here we compare the role of T-bet and STAT1 in the initiation and regulation of experimental autoimmune encephalomyelitis (EAE), a disease initiated by Th1 cells. T-bet–deficient mice immunized with myelin oligodendrocyte glycoprotein (MOG) were resistant to the development of EAE. This protection was also observed when T-bet−/− mice were crossed to the MOG-specific 2D2 T cell receptor transgenic strain. In contrast, although T-bet is downstream of STAT1, STAT1−/− mice were highly susceptible to EAE and developed more severe and accelerated disease with atypical neuropathologic features. The function of T-bet was dominant as mice deficient in both T-bet and STAT1 were also protected from EAE. CD4+ CD25+ regulatory T cells from these two mice strains were fully competent and do not explain the difference in disease susceptibility. However, enhanced EAE in STAT1−/− mice was associated with continued generation of IFN-γ–producing Th1 cells and up-regulation of selective chemokines responsible for the increased recruitment of macrophages and neutrophils in the central nervous system. Although the two transcription factors, STAT1 and T-bet, both induce IFN-γ gene transcription, our results demonstrate marked differences in their function in regulating pathogenic Th1 cell responses.
Examination of Msh6- and Msh3-deficient Mice in Class Switching Reveals Overlapping and Distinct Roles of MutS Homologues in Antibody Diversification
Authors: Li Ziqiang , Scherer Stefan J. , Ronai Diana , Iglesias-Ussel Maria D. , Peled Jonathan U. , Bardwell Philip D. , Zhuang Min , Lee KyeRyoung , Martin Alberto , Edelmann Winfried , Scharff Matthew D.
Published: July 2004

Somatic hypermutation and class switch recombination (CSR) contribute to the somatic diversification of antibodies. It has been shown that MutS homologue (Msh)6 (in conjunction with Msh2) but not Msh3 is involved in generating A/T base substitutions in somatic hypermutation. However, their roles in CSR have not yet been reported. Here we show that Msh6−/− mice have a decrease in CSR, whereas Msh3−/− mice do not. When switch regions were analyzed for mutations, deficiency in Msh6 was associated with an increase in transition mutations at G/C basepairs, mutations at RGYW/WRCY hotspots, and a small increase in the targeting of G/C bases. In addition, Msh6−/− mice exhibited an increase in the targeting of recombination sites to GAGCT/GGGGT consensus repeats and hotspots in Sγ3 but not in Sμ. In contrast to Msh2−/− mice, deficiency in Msh6 surprisingly did not change the characteristics of Sμ-Sγ3 switch junctions. However, Msh6−/− mice exhibited a change in the positioning of Sμ and Sγ3 junctions. Although none of these changes were seen in Msh3−/− mice, they had a higher percentage of large inserts in their switch junctions. Together, our data suggest that MutS homologues Msh2, Msh3, and Msh6 play overlapping and distinct roles during antibody diversification processes.
15-epi-lipoxin A4–mediated Induction of Nitric Oxide Explains How Aspirin Inhibits Acute Inflammation
Authors: Paul-Clark Mark J. , van Cao Thong , Moradi-Bidhendi Niloufar , Cooper Dianne , Gilroy Derek W.
Published: July 2004

The established model for the mechanism of action of aspirin is the inhibition of prostaglandin synthesis. However, this has never fully explained aspirin's repertoire of antiinflammatory properties. We found in acute pleuritis that aspirin, but not salicylate, indomethacin, or piroxicam, increased plasma nitric oxide (NO), which correlated with a reduction in inflammation. Inhibiting aspirin-elicited NO pharmacologically in this model nullified the antiinflammatory effects of aspirin. Moreover, aspirin was not antiinflammatory in either constitutive (eNOS) or inducible NO synthase (iNOS) knockout mice with IL-1β–induced peritonitis. It transpires that aspirin generates NO through its unique ability to trigger the synthesis of 15-epi-lipoxin A4. Aspirin and 15-epi-lipoxin A4 were shown to inhibit leukocyte trafficking in an NO-dependent manner using intravital microscopy on IL-1β–stimulated mouse mesentery. Not only did aspirin inhibit leukocyte–endothelial interaction in a manner similar to NO in wild-type mice but both aspirin and 15-epi-lipoxin A4 had markedly reduced effects on leukocyte–endothelial cell adherence in eNOS- and iNOS-deficient mice compared with wild type. Collectively, these data suggest that aspirin triggers the synthesis of 15-epi-lipoxin A4, which increases NO synthesis through eNOS and iNOS. This aspirin-elicited NO exerts antiinflammatory effects in the microcirculation by inhibiting leukocyte–endothelium interactions.
A Role for Msh6 But Not Msh3 in Somatic Hypermutation and Class Switch Recombination
Authors: Martomo Stella A. , Yang William W. , Gearhart Patricia J.
Published: July 2004

Somatic hypermutation is initiated by activation-induced cytidine deaminase (AID), and occurs in several kilobases of DNA around rearranged immunoglobulin variable (V) genes and switch (S) sites before constant genes. AID deaminates cytosine to uracil, which can produce mutations of C:G nucleotide pairs, and the mismatch repair protein Msh2 participates in generating substitutions of downstream A:T pairs. Msh2 is always found as a heterodimer with either Msh3 or Msh6, so it is important to know which one is involved. Therefore, we sequenced V and S regions from Msh3- and Msh6-deficient mice and compared mutations to those from wild-type mice. Msh6-deficient mice had fewer substitutions of A and T bases in both regions and reduced heavy chain class switching, whereas Msh3-deficient mice had normal antibody responses. This establishes a role for the Msh2-Msh6 heterodimer in hypermutation and switch recombination. When the positions of mutation were mapped, several focused peaks were found in Msh6−/− clones, whereas mutations were dispersed in Msh3−/− and wild-type clones. The peaks occurred at either G or C in WGCW motifs (W = A or T), indicating that C was mutated on both DNA strands. This suggests that AID has limited entry points into V and S regions in vivo, and subsequent mutation requires Msh2-Msh6 and DNA polymerase.
Settlement in Tax Evasion Prosecution
Authors: Macho‐Stadler Inés , Pérez‐Castrillo David
Published: July 2004

It is often argued that, even if optimal ex post, settlement dilutes deterrence ex ante. We analyse the interest for the tax authority of committing, ex ante, to a settlement strategy. We show that to commit to the use of settlements is ex ante optimal when the tax authority receives signals that provide statistical information about the taxpayers' true tax liability. The more informative the signal, the larger the additional expected revenue raised by the tax authority when using settlement as a policy tool.
Discretion in Tax Enforcement
Authors: Franzoni Luigi Alberto
Published: July 2004

This paper deals with the issue of whether the Revenue Service (RS) should be allowed, or even encouraged, to negotiate settlement agreements with taxpayers subject to examination. We consider the case in which the RS enjoys discretion at the settlement stage, its stance being guided by officers' professional judgment. We show that discretionary settlements serve a desirable function, as they allow the RS to better exploit taxpayer‐specific information and to take advantage of the bargaining power it can wield at the negotiation stage.
Constrained Efficient Fine‐cum‐Tax Rate Structures: The Case of Constant Relative Risk Aversion
Authors: Ueng K. L. Glen , Yang C. C.
Published: July 2004

This paper explores the possibility that fines and tax rates impose different welfare costs on different types of taxpayer, so that the government may want to apply different fine/tax rate treatments to different types of taxpayer. Under the assumption that taxpayers exhibit constant relative risk aversion, we characterize the constrained Pareto‐efficient fine/tax rate structure, showing that: (i) the co‐existence of compliers (the above‐ground economy) and evaders (the underground economy) is typical at the Pareto optimum, and (ii) Pareto efficiency requires compliers to face tax rates no higher and fines no lower than those faced by evaders.
Optimal Law Enforcement with Legal Aid
Authors: Garoupa Nuno , Stephen Frank H
Published: July 2004

The economic literature on enforcement is generally pessimistic concerning the use of legal aid. In this paper we show that legal aid can be a part of optimal law enforcement. The rationale behind our result is that with legal aid, in a system with legal or judicial error both guilty and innocent individuals are better off, because the marginal cost of defence expenditure is reduced. If, on average, legal aid helps the innocent more than the guilty, a government seeking to maximize social welfare will want to use it in order to increase deterrence.
Dispersal and individual quality in a long lived species
Authors: Cam Emmanuelle , Monnat J. Jean‐Yves , Royle Andrew
Published: July 2004

The idea of differences in individual quality has been put forward in numerous long‐term studies in long‐lived species to explain differences in lifetime production among individuals. Despite the important role of individual heterogeneity in vital rates in demography, population dynamics and life history theory, the idea of “individual quality” is elusive. It is sometimes assumed to be a static or dynamic individual characteristic. When considered as a dynamic trait, it is sometimes assumed to vary deterministically or stochastically, or to be confounded with the characteristics of the habitat. We addressed heterogeneity in reproductive performance among individuals established in higher‐quality habitat in a long‐lived seabird species. We used approaches to statistical inference based on individual random effects permitting quantification of heterogeneity in populations and assessment of individual variation from the population mean. We found evidence of heterogeneity in breeding probability, not success probability. We assessed the influence of dispersal on individual reproductive potential. Dispersal is likely to be destabilizing in species with high site and mate fidelity. We detected heterogeneity after dispersal, not before. Individuals may perform well regardless of quality before destabilization, including those that recruited in higher‐quality habitat by chance, but only higher‐quality individuals may be able to overcome the consequences of dispersal. Importantly, results differed when accounting for individual heterogeneity (an increase in mean breeding probability when individuals dispersed), or not (a decrease in mean breeding probability). In the latter case, the decrease in mean breeding probability may result from a substantial decrease in breeding probability in a few individuals and a slight increase in others. In other words, the pattern observed at the population mean level may not reflect what happens in the majority of individuals.
Trophic dynamics in a whole lake experiment: size‐structured interactions and recruitment variation
Authors: Persson Lennart , Byström Pär , Wahlström Eva , Westman Erika
Published: July 2004

Horizontal and vertical heterogeneity as a result of size‐structured processes are important factors influencing indirect effects in food webs. In a whole‐lake experiment covering 5 years, we added the intermediate consumer roach (Rutilus rutilus) to two out of four lakes previously inhabited by the omnivorous top predator perch (Perca fluviatilis). We focused our study on the direct consumption effect of roach presence on zooplankton (and indirectly phytoplankton) versus the indirect effect of roach on zooplankton (and phytoplankton) mediated via effects on perch reproductive performance. The patterns in zooplankton and phytoplankton abundances were examined in relation to population density of roach and perch including young‐of‐the‐year (YOY) perch in the light of non‐equilibrium dynamics. The presence of roach resulted in changed seasonal dynamics of zooplankton with generally lower biomasses in May–June and higher biomasses in July–August in roach lakes compared to control lakes. Roach presence affected perch recruitment negatively and densities of YOY perch were on average higher in control lakes than in treatment lakes. In years when perch recruitment did not differ between lakes as a result of experimental addition of perch eggs, total zooplankton biomass was lower in treatment lakes than in control lakes. Phytoplankton biomass showed a tendency to increase in roach lakes compared to control lakes. Within treatment variation in response variables was related to differences in lake morphometry in treatment lakes. Analyses of the trophic dynamics of each lake separately showed strong cascading effects of both roach and YOY perch abundance on zooplankton and phytoplankton dynamics. Consideration of the long transients in the dynamics of top predators (fish) in aquatic systems that are related to their long life span involving ontogenetic niche shifts is essential for making relevant interpretations of experimental perturbations. This conclusion is further reinforced by the circumstance that the intrinsic dynamics of fish populations may in many cases involve high amplitude dynamics with long time lags.
Relating niche and spatial overlap at the community level
Authors: Hofer Ulrich , Bersier Louis‐Félix , Borcard Daniel
Published: July 2004

If interspecific competition is a strong structuring force of communities, ecologically similar species should tend to have spatial ranges at local scale that do not overlap. Experimental testing of this hypothesis becomes impracticable with large communities. One possibility to tackle this issue is a correlational approach, by comparing the matrix of niche overlap with that of spatial overlap. The use of the standard Mantel test is however impaired by the non‐linearity in the relationship of the two descriptors: in a competitively structured assemblage, species with high niche overlap are expected to be segregated spatially, but species with small niche overlap may or may not exhibit high spatial overlap. To overcome this problem, we devised an original randomization test, which was run for three data‐sets comprising frogs, lizards, and birds along altitudinal gradients. The test yielded intriguing results: reptiles and birds revealed an adjustment that would reduce the potential for interspecific competition, while amphibians showed the opposite trend, that is, ecologically similar species co‐occurred more than expected by chance. Frogs may be more constrained by resource requirements, possibly breeding sites, than by competition. Our test will help to assess the generality of this pattern with other data‐sets.
The distribution of Eurasian badger,Meles meles, setts in a high‐density area: field observations contradict the sett dispersion hypothesis
Authors: Macdonald D. W. , Newman C. , Dean J. , Buesching C. D. , Johnson P. J.
Published: July 2004

Are setts significant determinants of badger socio‐spatial organisation, and do suitable sett sites represent a limited resource, potentially affecting badger distributions? The factors determining diurnal resting den, or sett, location and selection by Eurasian badgersMeles melesL. were investigated in Wytham Woods, Oxfordshire. 279 sett sites were located. The habitat parameters that were associated with the siting of these setts were analysed and associations were sought between sett location and character and the body condition and body weight of resident badgers Habitat characteristics in the vicinity of setts were significantly different from randomly selected points. Badgers preferentially selected sites with sandy, well‐drained soils, situated on NW‐facing, convex and moderately inclined slopes at moderate altitude. There was no evidence that sett morphology (number of entrances, sett area, number of hinterland latrines) was affected by the surrounding sett site habitat characteristics. Mean body weight was significantly higher for badgers occupying territories with setts in sandy soils, situated on NW‐facing slopes, than in territories with less optimal sett characteristics. Contrary to the hypothesis that the availability of sett sites was limiting, and therefore that sett dispersion dictates the spatial and social organisation of their populations, the badgers were clearly able to excavate new setts. On our measures, these new setts were not inferior to old established ones, despite occupying subsequently exploited sites; the badgers utilising these new setts had neither lighter body weights nor poorer body condition scores. During the period of our study badgers have manifestly been able to dig numerous new setts; as satisfactory sites still remain available, this indicates that suitable sett sites have not yet become a limiting resource. There was no relationship between sett age and the characteristics of the site in which it was dug, as suitable sites were not limiting. Significantly, population expansion during the decade 1987–1997 was not constrained by lack of setts, rather the main proliferation in setts occurred after the population size had peaked in 1996. Some implications for the management and conservation of the Eurasian badger are considered.
Modelling mortality and dispersal: consequences of parameter generalisation on metapopulation dynamics
Authors: Mennechez Gwénaëlle , Petit Sandrine , Schtickzelle Nicolas , Baguette Michel
Published: July 2004

Modelling dispersal is a fundamental step in the design of population viability analyses. Here, we address the question of the generalisation of population viability analysis models across landscapes by comparing dispersal between two metapopulations of the bog fritillary butterfly (Proclossiana eunomia) living in similar highly fragmented landscapes (<1% of suitable habitat in 9 km2). Differences in dispersal patterns were investigated using the virtual migration (VM) model, which was parameterised with capture–mark–recapture data collected during several years in both landscapes. The VM model allows the estimation of 6 parameters describing dispersal and mortality as well as the simulation of dispersal in the landscapes. The model revealed large differences in the VM parameter estimates between the two landscapes and consequently, simulations indicated differential rates of emigration and dispersal mortality. Furthermore, results from crossed‐simulations i.e. simulations performed in one of the landscape but using parameter estimates from the other landscape emphasize that dispersal parameters are very specific to each metapopulation and to their landscape. Hence, we urge conservation biologists to be cautious with such parameter generalisations, even for the same species in comparable landscapes.
Parasitism, developmental plasticity and bilateral asymmetry of wing feathers in alpine swift,Apus melba, nestlings
Authors: Bize Pierre , Roulin Alexandre , Richner Heinz
Published: July 2004

The hypothesis that developmental instability is a cost of developmental plasticity is explored using the alpine swift (Apus melba) as a model organism. In a previous study, experimentally parasitized nestlings showed a reduced wing growth rate in the first half of the rearing period when parasites were abundant (i.e. peak infestation) and an accelerated growth rate (i.e. compensatory growth) in the second half when parasites decreased in number. This suggests that alpine swifts are able to adjust growth rate in relation to variation in parasite loads. Because developmental plasticity may entail fitness costs, the energy required to sustain compensatory growth may be invested at the expense of developmental stability, potentially resulting in larger deviations from symmetry in paired, bilateral traits (i.e. fluctuating asymmetry, FA). This hypothesis predicts higher FA in parasitized than deparasitized nestlings because of compensatory growth, and hence individuals sustaining the highest level of compensatory growth rate should exhibit the highest FA levels. Another non‐mutually exclusive hypothesis argues that parasites directly cause FA by diverting energy required by host for maintenance and growth, and predicts that individuals suffering the most from parasitism during peak infestation should exhibit the highest FA levels. The present study shows that wing feathers of experimentally parasitized nestlings were more asymmetrical than those of experimentally deparasitized ones 50 days after hatching. Furthermore, in parasitized individuals FA was negatively correlated with wing growth rate during the period of peak infestation but not during the period of compensatory growth. These findings suggest that developmental homeostasis is more sensitive to parasites than to compensatory growth.
Competition, predation and species responses to environmental change
Authors: Jiang Lin , Kulczycki Alexander
Published: July 2004

Despite much effort over the past decade on the ecological consequences of global warming, ecologists still have little understanding of the importance of interspecific interactions in species responses to environmental change. Models predict that predation should mitigate species responses to environmental change, and that interspecific competition should aggravate species responses to environmental change. To test this prediction, we studied how predation and competition affected the responses of two ciliates, Colpidiumstriatum and Parameciumtetraurelia, to temperature change in laboratory microcosms. We found that neither predation nor competition altered the responses of Colpidiumstriatum to temperature change, and that competition but not predation altered the responses of Paramecium tetraurelia to temperature change. Asymmetric interactions and temperature‐dependent interactions may have contributed to the disparity between model predictions and experimental results. Our results suggest that models ignoring inherent complexities in ecological communities may be inadequate in forecasting species responses to environmental change.